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The first film in the series, "The Mortal Instruments: City of Bones," is due out in August

Producers Constantin Film and Unique Features must be confident in their “The Mortal Instruments: City of Bones,” due Aug. 23. They have just signed the two stars, Lily Collins and Jamie Campbell Bower, in the sequel: “The Mortal Instruments: City of Ashes.”

The films are based on a successful series of young-adult books, five of which are in print with another set to hit shelves next March. More than 16 million copies of the series have been sold worldwide.

In the books, second book, Clary Fray (Collins) is a teenager whose mother is kidnapped; she turns to Shadowhunter Jace (Campbell Bower), a half-angel, half-human warrior, to help get her back — only to discover that she is a Shadowhunter, as well.

ScreenGems and parent company Sony will distribute the first film, which Constantin Film, Sony and Unique Features produced. Constantin and Unique Features will produce the sequel as well, which Mister Smith, which announced the sequel, will begin to sell at the Cannes Film Festival next week.

“We are outstandingly proud of what has been achieved on 'The Mortal Instruments: City of Bones' – and what better proof would there be than putting the next installment of Cassandra Clare’s phenomenal vision – 'City of Ashes' – into production now,” Martin Moszkowicz, a member of the executive board of Constantin Film and executive producer on the film, said in a statement.

Harald Zwart, who directed “The Karate Kid” and the first film in the series, will direct the second. Jessica Postigo Paquette, who wrote the first, also scripted the second. Principal photography will begin in the fall.